Mayor Jean Quan, standing in front of a mural of Carlos Nava, a 3-year-old who was killed by a stray bullet in 2011, speaks on the recent violent crimes in Oakland. The police chief tied many of them to last year's killing of a 16-year-old girl.

Photo: Michael Short, Special To The Chronicle

Mayor Jean Quan, standing in front of a mural of Carlos Nava, a...

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Mayor Jean Quan is seen with other members of her administration as they attend a press conference held on International Blvd. Oakland police, Mayor Jean Quan and City Administrator held a news conference to discuss the ongoing violence gripping Oakland, Monday January 14th, 2013.

Photo: Michael Short, Special To The Chronicle

Mayor Jean Quan is seen with other members of her administration as...

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Burton Gerstel(L) of San Leandro, who's daughter Raquel Gerstel, 15, was murdered in Oakland recently, attended the press conference held on International Blvd. in Oakland, CA. Oakland police, Mayor Jean Quan and City Administrator held a news conference to discuss the ongoing violence gripping Oakland, Monday January 14th, 2013.

Photo: Michael Short, Special To The Chronicle

Burton Gerstel(L) of San Leandro, who's daughter Raquel Gerstel,...

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Mayor Jean Quan and City Administrator held a news conference on International Blvd. to discuss the ongoing violence gripping Oakland, CA Monday January 14th, 2013.

Photo: Michael Short, Special To The Chronicle

Mayor Jean Quan and City Administrator held a news conference on...

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Police Chief Howard Jordan, appearing with Mayor Jean Quan, attributed two of Friday's four killings to the feuding groups.

Photo: Michael Short, Special To The Chronicle

Police Chief Howard Jordan, appearing with Mayor Jean Quan,...

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Oakland Police Chief Howard Jordan stands in front of a mural of 3 year old homicide victim Carlos Nava on International Blvd. as he addresses the gathered media. Oakland police, Mayor Jean Quan and City Administrator held a news conference to discuss the ongoing violence gripping Oakland, Monday January 14th, 2013.

Photo: Michael Short, Special To The Chronicle

Oakland Police Chief Howard Jordan stands in front of a mural of 3...

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City Councilman Noel Gallo, who represents Fruitvale, was among the officials at the news conference.

Photo: Michael Short, Special To The Chronicle

City Councilman Noel Gallo, who represents Fruitvale, was among the...

Nearly all the violent crimes in Oakland in the last few months, including two killings over the weekend, have been committed as part of a "war" between rival groups that was sparked by the slaying of a girl last summer, Police Chief Howard Jordan said Monday.

Jordan said "about 90 percent" of the killings, robberies, shootings and other "senseless acts of violence" in the city since mid-2012 can be directly tied to the killing of a girlfriend of one of the combatants.

Over time, the warring factions have become increasingly violent and have grown in number, sometimes by merging with other groups, Jordan said at a news conference called in response to an outbreak of gunfire over the weekend.

Oakland's totals for homicides, robberies and other violent crimes all spiked last year. It was not clear how Jordan attributed 90 percent of the crimes late in the year to the warring groups; Oakland typically sees 200 to 300 robberies per month, and the vast majority go unsolved.

Girl's killing

The chief did not provide details about the original shooting that he said set off the fighting. But law enforcement sources said he was referring to the Aug. 8 killing of Taiteanna Turner, a 16-year-old girl who was shot dead outside a liquor store on Talbot Avenue in East Oakland.

Turner was with a 23-year-old man and was apparently not the intended target of the killer, said the sources, who asked not to be identified because they were not authorized to speak about the matter. No one has been arrested for her slaying.

Other members of Turner's family had already fallen victims to gun violence in Oakland. Her father was slain in 2008, and her 15-year-old cousin was shot to death in East Oakland in July.

Former allies

Three sources said the two East Oakland groups at the center of the violence are relatively new to the scene and once were on more friendly terms. One is known as the "Case Gang" and the other, much larger group is known as the "Money Team," the sources said.

Among the violence attributed to the feud, two sources said, was the Aug. 16 killing of Demariae Clay, 25, in a KFC drive-through in East Oakland. Clay's 19-year-old girlfriend was injured.

Charged with murder in the case are Terry Austin and Anthony Paige, who are each 27 and allegedly affiliated with the Case Gang, the sources said.

Members of the two groups were among the targets of a gang intervention program that authorities and community leaders launched in the fall called Operation Ceasefire.

On Oct. 18, several alleged members of the groups were summoned to a meeting known as a "call-in" at an East Oakland church, where a carrot-and-stick approach was used. They were offered social services but also told to end the gun violence.

"We told them, 'Look, you guys need to put the guns down and tell your buddies to put the guns down. And if you don't, we're going to make a special effort to focus on you,' " said Alameda County prosecutor John Creighton, who was there along with police, parole and probation officers, federal prosecutors, pastors and other community advocates.

Weekend violence

Jordan attributed two of the four killings that happened in Oakland on Friday to groups involved in the fighting, but did not elaborate.

A suspect in one of the four killings - a shooting death on West Street in West Oakland - has been arrested, and another is being sought with the help of the U.S. Marshals Service, Jordan said without giving details.

The weekend violence included shootings that wounded a total of 11 people, five of them at a party for a woman celebrating her 25th birthday. The mayhem prompted Vice Mayor Larry Reid and a coalition of pastors to urge the city to declare a state of emergency that could make Oakland eligible for additional money that would pay for help from other police agencies.

"We need help," Reid said, adding that he's never felt as unsafe in Oakland in 31 years as he does now.

Chief skeptical

Jordan downplayed the effectiveness of such a declaration, saying any money the city received would pay for only a few days of mutual aid.

"We're not going to make a formal request, because we feel that we've been operating currently under a state of emergency," Jordan said.

Oakland police trying to find people involved in the violence are already being assisted by schools and housing police, the California Highway Patrol and agents with the federal Bureau of Alcohol, Tobacco, Firearms and Explosives, Jordan said. CHP officers are patrolling city streets on weekends, and Jordan said the city has asked the state police agency to stay on beyond Jan. 31, when its contract with Oakland is supposed to end.

In addition, Reid and Councilwoman Libby Schaaf have proposed hiring 10 Alameda County sheriff's deputies and one supervisor to help on weekends. They also want to authorize a new police academy class in addition to one already training 55 recruits and to hire more police service technicians, who handle administrative tasks such as removing abandoned cars, which could free up officers for more pressing calls for service.

Jordan said the long-term, "more sustainable" solution is to hire more police officers who will be around "for the next 25 years." The chief has said the department is understaffed; layoffs and other reductions have shrunk the force from 837 in 2008 to about 616 now.